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Date: Mon, 10 Apr 2017 18:12:40 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Arnd Bergmann <arnd@...db.de>, Dave Hansen <dave.hansen@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Oleg Nesterov <oleg@...hat.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Kees Cook <keescook@...omium.org>, Rik van Riel <riel@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>, linux-s390@...r.kernel.org,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
x86@...nel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 4/4] arm64/syscalls: Architecture specific
pre-usermode check
On Mon, Apr 10, 2017 at 09:44:20AM -0700, Thomas Garnier wrote:
> Disable the generic pre-usermode check in favor of an optimized
> implementation. This patch adds specific checks on user-mode return path
> to make it faster and smaller.
>
> The address limit is checked on each syscall return path to user-mode.
> If it was changed, a generic handler is called to stop the kernel on an
> explicit check.
>
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---
> Based on next-20170410
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/entry.S | 13 +++++++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 9b8fcab7da56..3f9e8e7d9376 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -24,6 +24,7 @@ config ARM64
> select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
> select ARCH_WANT_FRAME_POINTERS
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> + select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
> select ARM_AMBA
> select ARM_ARCH_TIMER
> select ARM_GIC
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 43512d4d7df2..bdd094c7837a 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -744,6 +744,8 @@ ENDPROC(cpu_switch_to)
> ret_fast_syscall:
> disable_irq // disable interrupts
> str x0, [sp, #S_X0] // returned x0
> + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
> + tbnz x2, #63, addr_limit_fail
> ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
> and x2, x1, #_TIF_SYSCALL_WORK
> cbnz x2, ret_fast_syscall_trace
> @@ -771,6 +773,9 @@ work_pending:
> */
> ret_to_user:
> disable_irq // disable interrupts
> + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
> + tbnz x2, #63, addr_limit_fail
> +
Nitpick: unnecessary empty line added.
> ldr x1, [tsk, #TSK_TI_FLAGS]
> and x2, x1, #_TIF_WORK_MASK
> cbnz x2, work_pending
> @@ -780,6 +785,14 @@ finish_ret_to_user:
> ENDPROC(ret_to_user)
>
> /*
> + * Address limit was incorrect before returning in user-mode which could be
> + * used to elevate privileges. Call the generic handler to stop the kernel on
> + * the appropriate check. This function does not return.
> + */
> +addr_limit_fail:
> + bl address_limit_check_failed
You could do a "b address_limit_check_failed" rather than "bl" since we
don't care about returning here (and a nitpick: insert tab between "b"
and "address_limit_check_failed").
With the above:
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
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